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Case Study: black and white and spread all over
• In 1988, Zebra mussels were accidentally introduced to Lake St. Clair
­In discharged ballast water
• By 2010, they had invaded 30 states
­No natural predators, competitors, or parasites
• They cause millions of dollars of damage to property each year
Species interactions
• Species interactions are the backbone of communities • Natural species interactions:
­Competition = both species are harmed
­Exploitative = one species benefits and the other is harmed
­Predation, parasitism, and herbivory ­Mutualism = both species benefit
Competition • Competition = multiple organisms seek the same limited resources
­Food, space, water, shelter, mates, sunlight
• Intraspecific competition = between members of the same species
­High population density = increased competition
• Interspecific competition = between members of 2 or more species
­Strongly affects community composition
­Leads to competitive exclusion or species coexistence
Results of interspecific competition
• Competitive exclusion = one species completely excludes another species from using the resource
­Zebra mussels displaced native mussels in the Great Lakes
• Species coexistence = neither species fully excludes the other from resources, so both live side by side
­This produces a stable point of equilibrium, with stable population sizes
­Species minimize competition by using only a part of the available resource (niche)
Niche: an individual’s ecological role
• Fundamental niche = the full niche of a species
• Realized niche = the portion of the fundamental niche that is actually filled
­Due to competition or other species’ interactions
Resource partitioning
• Resource partitioning = species use different resources
­Or they use shared resources in different ways
­Ex: one species is active at night, another in the day
­Ex: one species eats small seeds, another eats large seeds
Character displacement
• Character displacement = competing species diverge in their physical characteristics
­Due to the evolution of traits best suited to the resources they use
­Results from resource partitioning
• Birds that eat larger seeds evolve larger bills
­Birds that eat smaller seeds evolve smaller bills
Competition is reduced when two species become more different
Exploitation: predation
• Exploitation = one member exploits another for its own gain (+/­ interactions)
­Predation, parasitism, herbivory
• Predation = process by which individuals of one species (predators) capture, kill, and consume individuals of another species (prey)
­Structures food webs
­The number of predators and prey influences community composition Zebra mussel predation on phytoplankton
• Zebra mussels eat phytoplankton and zooplankton
­Both populations decrease in lakes with zebra mussels
• Zebra mussels don’t eat cyanobacteria ­Population increases in lakes with zebra mussels
• Zebra mussels are becoming prey for some North American predators:
­Diving ducks, muskrats, crayfish, flounder, sturgeon, eels, carp, and freshwater drum
Effects of predation on populations
• Increased prey populations increase predators
­Predators survive and reproduce
• Increased predator populations decrease prey
­Predators starve
• Decreased predator populations increase prey populations
Predation has evolutionary ramifications
• Natural selection leads to evolution of adaptations that make predators better hunters
• Individuals who are better at catching prey:
­Live longer, healthier lives ­Take better care of offspring
• Prey face strong selection pressures: they are at risk of immediate death
­Prey develop elaborate defenses against being eaten
Defenses against being eaten
Exploitation: parasitism
• Parasitism = a relationship in which one organism (parasite) depends on another (host) ­For nourishment or some other benefit
­The parasite harms, but doesn’t kill, the host
• Some are free­living
­Infrequent contact with their hosts
­Ticks, sea lampreys
• Some live within the host
­Disease, tapeworms
Parasites evolve in response to each other
• Parasitoids = insects that parasitize other insects killing the host
• Coevolution = hosts and parasites become locked in a duel of escalating adaptations
­Has been called an evolutionary arms race ­Each evolves new responses to the other
­It may not be beneficial to the parasite to kill its host
Exploitation: herbivory
• Herbivory = animals feed on the tissues of plants
­Widely seen in insects
• May not kill the plant
­But affects its growth and survival
• Defenses against herbivory include:
­Chemicals: toxic or distasteful
­Thorns, spines, or irritating hairs
­Other animals: protect the plant
Mutualism
• Two or more species benefit from their interactions (+/+)
• Symbiosis = mutualism in which the organisms live in close physical contact
­Each partner provides a service the other needs (food, protection, housing, etc.)
­Microbes within digestive tracts
­Mycorrhizae: plant roots and fungi
­Coral and algae (zooxanthellae)
• Pollination = bees, bats, birds and others transfer pollen from one flower to another, fertilizing its eggs
Pollination
In exchange for the plant nectar, the animals pollinate plants, which allows them to reproduce
Merlin Tuttle Merlin Tuttle Relationships with no effect on one member
• Amensalism = a relationship in which one organism is harmed while the other is unaffected (­/0)
­Difficult to confirm, because usually one organism benefits from harming another
­Allelopathy = certain plants release harmful chemicals
­Example: Black Walnut Trees
­Or, is this a way to outcompete another for space and kill my tomatoes?
• Commensalism = a relationship in which one organism benefits, while the other remains unaffected (+/0)
­Example: Clown fish Ecological communities
• Community = an assemblage of populations of organisms living in the same place at the same time
­Members interact with each other
­Interactions determine the structure, function, and species composition of the community
• Community ecologists are people interested in how: ­Species coexist and relate to one another
­Communities change, and why patterns exist Energy passes through trophic levels
• One of the most important species interactions ­Who eats whom?
• Matter and energy move through the community
• Trophic levels = rank in the feeding hierarchy
­Producers (autotrophs)
­Consumers
­Detritivores and decomposers
Producers: the first trophic level
• Producers, or autotrophs (“self­feeders”) = organisms capture solar energy for photosynthesis to produce sugars
­Green plants
­Cyanobacteria
­Algae
• Chemosynthetic bacteria use the geothermal energy in hot springs or deep­sea vents to produce their food
Consumers: consume producers
• Primary consumers = second trophic level
­Organisms that consume producers
­Herbivores consume plants
­Deer, grasshoppers
• Secondary consumers = third trophic level
­Organisms that prey on primary consumers
­Carnivores consume meat ­Fish, rodents
Consumers occur at higher trophic levels
• Tertiary Consumers = fourth trophic level
­Predators at the highest trophic level
­Consume secondary consumers
­Are also carnivores
­Hawks, owls
• Omnivores = consumers that eat both plants and animals
Detritivores and decomposers
• Organisms that consume nonliving organic matter
­Enrich soils and/or recycle nutrients found in dead organisms
• Detritivores = scavenge waste products or dead bodies
­Millipedes, soil insects
• Decomposers = break down leaf litter and other non­
living material
­Fungi, bacteria
­Enhance topsoil and recycle nutrients
Energy, biomass, and numbers decrease
• Most energy organisms use is lost as waste heat through cellular respiration
­Less and less energy is available in each successive trophic level
­Each level contains only 10% of the energy of the trophic level below it
• There are also far fewer organisms and less biomass (mass of living matter) at the higher trophic levels
A human vegetarian’s ecological footprint is smaller than a meat­eater’s footprint
Pyramids of energy, biomass, and numbers
Food webs show relationships and energy flow
• Food chain = a series of feeding relationships
• Food web = a visual map of feeding relationships and energy flow
­Includes many different organisms at all various levels
­Greatly simplified; leaves
out most species
Some organisms play big roles
• Community dynamics are complex
­Species interactions differ in strength and over time
• Keystone species = has a strong or wide­reaching impact ­Far out of proportion to its abundance
• Removal of a keystone species has substantial ripple effects ­Alters the food chain
Species can change communities
• Trophic Cascade = predators at high trophic levels indirectly affect populations at low trophic levels
­By keeping species at intermediate trophic levels in check
­Extermination of wolves led to increased deer populations, which overgrazed vegetation and changed forest structure
• Ecosystem engineers = physically modify the environment
­Beavers, prairie dogs, ants, zebra mussels
Communities respond to disturbances
• Communities experience many types of disturbance
­Removal of keystone species, spread of invasive species, natural disturbances
­Human impacts cause major community changes
• Resistance = community of organisms resists change and remains stable despite the disturbance
• Resilience = a community changes in response to a disturbance, but later returns to its original state
• A disturbed community may never return to its original state
Succession
• Succession = the predictable series of changes in a community ­Following a disturbance • Primary succession = disturbance removes all vegetation and/
or soil life
­Glaciers, drying lakes, volcanic lava
• Pioneer species = the first species to arrive in a primary succession area (i.e. lichens)
Ian Plant
Secondary succession
• Secondary succession = a disturbance dramatically alters, but does not destroy, all local organisms
­The remaining organisms form “building blocks” which help shape the process of succession
­Fires, hurricanes, farming, logging
• Climax community = remains in place with few changes
­Until another disturbance restarts succession
Communities may undergo shifts
• The dynamics of community change are more variable and less predictable than thought
­Conditions at one stage may promote another stage
­Competition may inhibit progression to another stage
­Chance factors also affect changes
• Phase (regime) shift = the overall character of the community fundamentally changes
­Some crucial threshold is passed, a keystone species is lost, or an exotic species invades
­i.e. overfishing and depletion of fish and turtles has allowed algae to dominate corals
Invasive species threaten stability
• Invasive species = non­native (exotic) organisms that spread widely and become dominant in a community
­Introduced deliberately or accidentally from elsewhere
­Growth­limiting factors (predators, disease, competitors, etc.) are removed or absent
­They have major ecological effects
­Chestnut blight from Asia wiped out American chestnut trees
• Some species help people (i.e., European honeybees)
Two invasive mussels
Controlling invasive species
• Techniques to control invasive species
­Removing them manually
­Applying toxic chemicals
­Drying them out
­Depriving them of oxygen
­Stressing them with heat, sound, electricity, carbon dioxide, or ultraviolet light
• Control and eradication are hard and expensive
Prevention, rather than control, is the best policy
Altered communities can be restored
• Humans have dramatically changed ecological systems
­Severely degraded systems cease to function
• Ecological restoration = efforts to restore communities
• Restoration is informed by restoration ecology = the science of restoring an area to an earlier condition
­To restore the system’s functionality (i.e. filtering of water by a wetland)
­It is difficult, time­consuming, and expensive
• It is best to protect natural systems from degradation in the first place
Restoration efforts
• Prairie restoration = replanting native species, controlling invasive species
• The world’s largest project = Florida Everglades
­Flood control and irrigation removed water
­Populations of wading birds dropped 90­95%
­It will take 30 years
and billions of dollars to restore natural water flow
Widely separated regions share similarities
• Biome = major regional complex of similar communities recognized by:
­Plant type and vegetation structure
Multiple factors determine a biome • The type of biome depends on abiotic factors ­Temperature, precipitation, soil type, atmospheric circulation
• Climatographs = a climate diagram showing: ­An area’s mean monthly temperature and precipitation
­Similar biomes occupy similar latitudes
Aquatic systems have biome­like patterns
• Various aquatic systems comprise distinct communities
­Coastlines, continental shelves ­Open ocean, deep sea ­Coral reefs, kelp forests
• Some coastal systems (estuaries, marshes, etc.) have both aquatic and terrestrial components
• Aquatic systems are shaped by
­Water temperature, salinity, and dissolved nutrients
­Wave action, currents, depth, light levels ­Substrate type, and animal and plant life